Can an invisibility cloak protect our vulnerable coasts?

Last year scientists created an invisibility cloak that bent light around an object, as if it weren’t there, in two dimensions. Work is underway on creating an invisibility cloak for visible light that works in three dimensions.

Light is a wave. So are ocean waves. Might a similar technology therefore apply to the sea? And therefore might we be able to protect oil rigs and potentially even islands? Maybe.

M. Farhat, S. Enoch, S. Guenneau and A.B. Movchan

Laboratory experiments show that obstacles arranged in fluids in certain patterns can effectively make objects they surround invisible to waves.

The researchers have built a prototype 10 centimeters across for testing in a wave tank. Concentric rings of rigid pillars form a labyrinth of radial and concentric corridors. It may look like waves could pass easily along the radial corridors to the cloak’s center. But they interact with the pillars, producing forces that pull water along the concentric corridors instead.

“Basically, the cloak behaves like a whirlpool,” says Sebastian Guenneau at the University of Liverpool, UK. “The further you go into the whirlpool, the faster you rotate.”

The spinning rate increases close to the cloak’s centre where the concentric corridors are narrower, making the forces greater, he explains.

As the water whizzes around the cloak, the waves are flung out again along the radial corridors. “If you imagine water entering the cloak from the north, some leaves the cloak to the east, and some leaves to the west, but most is thrown out at the south,” says Guenneau.

This is a nice analogy for the same way metamaterials work with light. But is it practical? I have a hard time seeing such structures practicably being built around deep water oil platforms. It also seems impractical for any decent sized stretch of coastline.

But it’s a most intriguing idea and offers some insight into how metamaterials really work.